1. Field of the Invention
This invention relates to high bandwidth communication in the back-plane of interconnected circuit-board-based systems, and, more particularly, to an integrated planar polymer waveguide-based architecture for low-loss, low-crosstalk optical signal routing in such hardware.
2. Description of the Related Art
The aggregate bit rates used to transmit information in servers, routers, and high-bandwidth computing systems has steadily increased for many years and is expected to continue to increase for the foreseeable future. Electrical interconnects are conventionally used to transmit information between elements in these computing systems. For example, electrical backplanes typically use high-bandwidth serial connections to facilitate communication between computing elements mounted on cards, such as processor cards, memory cards, I/O cards, and the like. Although serial electrical interconnects have performed admirably for many years, the increasing speed and complexity of data systems have tested the limits of serial electrical interconnect technology. For example, electrical backplanes with high-bandwidth serial connections face difficult microwave engineering challenges when these connections are used to transmit at high bit rates, e.g., above 10 Gbps. Parallel electrical interconnects may address some of the limitations imposed by microwave engineering, but these approaches require complex spatial routing. Generally speaking, electrical signaling at these frequencies is constrained by electromagnetic interference and crosstalk, as well as microwave regeneration, splitting, and routing needs.
Serial optical interconnections are capable of supporting bit rates in excess of 10 Gbps. Furthermore, optical interconnects may be able to improve bandwidth-length products, eliminate electromagnetic interference effects and reduce thermal costs. Multimode polymer waveguides that can be integrated on printed circuit boards (PCBs) have been of particular interest at least in part because they offer a low cost and highly efficient solution for high speed interconnects while allowing for reduced connectorisation costs owing to relaxed alignment tolerances. Organo-functional siloxane based resins and polymers, such as polydimethyl siloxane (PDMS), exhibit low loss at data communication wavelengths (0.03-0.05 dB/cm at 850 nm) and possess excellent mechanical and thermal properties. For example, organo-functional siloxane based resins and polymers can withstand temperatures in excess of 250° C., the temperature that is typically needed for lead-free solder reflow. However, interference and crosstalk between serial optical interconnects needs to be demonstrably improved in comparison with the conventional electrical interconnects to avoid limiting the aggregate data rate of devices formed using optical interconnects. Although the incumbent electrical technology in the market has been innovative in improving electrical systems performances, it has not taken due account of the proven competencies (particularly in terms of practical manufacturable implementation and cost-performance metrics) of emergent optical technology to address these challenges and create a competitive value proposition.